The fuel pump diaphragm in that $4.80 kit is mylar - it's intended for use where there is ether and/or ethanol in the fuel, as in the US. I haven't tried using a mylar diaphragm - I've seen scattered reports that it is more troublesome than the conventional one, in that it doesn't always work when installed as casually as a conventional one is installed. Since your metering needle is OK, and you don't have signs of lean mixture, you have a good chance of success just by replacing the metering and fuel pump diaphragms with conventional ones the same as the original ones. There are no indications of any problem with your original fuel pump diaphragm, but since you will have a new one, and they do age, it seems appropriate to fit it in the interests of long term reliability.
